1. Field of the Invention
This invention relates to an improved polycondensation process, the improvement comprising a process sequence wherein a two-phase admixture comprising (a) an organic phase containing an aromatic dihydroxy compound, an inert solvent, a polycondensation catalyst, and a chain stopper, and (b) an aqueous phase containing a solution of an alkali metal hydroxide is equilibrated and maintained at a specific pH range prior to the introduction of a carbonyl halide, the improvement comprising adding and reacting the carbonyl halide in the two-phase organic aqueous phase admixture in accordance with the following improved process parameters:
(1) a pH range of 11 to 13, PA1 (2) a reaction temperature range of from 15.degree. to 40.degree. C., PA1 (3) a carbonyl halide rate of addition of 0.03 to 0.3 moles/minute per mole of aromatic dihydroxy compound, and PA1 (4) a chain-stopper content of 0.02 to 0.05 moles per mole of aromatic dihydroxy compound. PA1 (i) an organic phase containing a non-sterically-hindered aromatic dihydroxy compound, an inert solvent, a polycondensation catalyst, a chain-stopper, and optionally, a sterically-hindered aromatic dihydroxy compound, PA1 (ii) an aqueous phase containing a solution of an alkali metal hydroxide having a pH within the range of from 11 to 13, PA1 (iii) adding and reacting a carbonyl halide with the non-sterically-hindered aromatic dihydroxy compound plus any optional sterically-hindered aromatic dihydroxy compound at PA1 (a) R is a C.sub.1-10 alkyl, C.sub.4-10 cycloalkyl, or C.sub.6-10 aryl group, including mixtures thereof. PA1 (b) R.sub.a is a C.sub.3-12 alkylene or C.sub.4-12 cycloalkylene group, including mixtures thereof, PA1 (c) R.sub.b is a C.sub.1-10 alkyl or C.sub.4-10 cycloalkyl group, including mixtures thereof, and
The resulting aromatic polycarbonates exhibit improved chemical and physical properties including a novel combination of a weight average molecular weight (Mw) range of from about 25,000 to 65,000 and a monocarbonate content of less than about 400 parts per million.
2. Description of the Prior Art
In general, interfacial polycondensation publications including "The Encyclopedia of Polymer Science," Vol. 10 (1969), "Chemistry and Physics of Polycarbonates, Polymer Reviews", H. Schnell, Vol. 9, John Wiley & Sons, Inc. (1964); "Polycarbonates", Christopher N. Fox, Rheinhold Corporation of New York, (1962); among other publications, including U.S. patents, e.g., U.S. Pat. Nos. 2,970,131; 3,028,365; 3,173,891; 3,275,601; 3,318,845,; and 3,989,672, report generally effective interfacial polycondensation processes.
Moyer, Jr. et al. in U.S. Pat. No. 2,970,131 describes a 2-step interfacial polycondensation polycarbonate process where the first step is carried out at a controlled pH range of 10.5-11.55, at a controlled temperature of 20.degree.-30.degree. C. to form an intermediate polymer which is subsequently bodied (equilibrated to a high molecular weight polycarbonate in the presence of a phase transfer agent (e.g. a quarternary ammonium compound) again under controlled reaction temperatures of 20.degree.-30.degree. C. Moyer states that the nature of the polycarbonate formed is independent of the length of time permitted for phosgenation so long as the pH of the reaction system is maintained within limits of 10.5 to 11.55. Moyer, Jr's Examples describe phosgenation reactions carried out over time periods of from 1 hour-45 minutes (minimum) to 10 hours-55 minutes (maximum). Moyer, Jr. et al. further describes that large excesses of sodium hydroxide lead to several side reactions contributing to decreased process efficiency and inferior final polymer product. Moyer also states that when chain-stoppers, e.g. para-phenylphenol, are used to control molecular weight, polymers having narrow limits are found which are of particular interest.
Fry et al. U.S. Pat. No. 3,173,891 describes a 2-step interfacial poly-condensation polycarbonate process which overcomes some of the defficiencies associated with the Moyer, Jr. et al. U.S. Pat. No. 2,970,131 by conducting the polycondensation reaction at a pH range of 10.5-11.8, preferably from 10.8-11.3, at a temperature of 20.degree.-30.degree. C., in the presence of a tertiary amine and para-phenylphenol. Fry states that the amine and p-phenylphenol combination functions as a unique bodying catalyst and chain growth terminator, a combination which cooperates to produce polycarbonates having the same desired molecular weight from batch to batch, even though reaction variables such as temperature and length of phosgenation vary widely.
Fry et al. like Moyer, Jr. et al. describes the 2-step process as contributing to a substantially lessened extent of side reaction occurrence so that greater latitude is possible with respect to such variables as phosgene addition rate, total phosgene addition time, reaction temperature, and time lapse between phosgene addition and subsequent isolation and purification of the final polycarbonate product. Like Moyer, Jr., Fry's rate of phosgenation is slow and is carried out over a 1 hour and 45 minutes time period.
Vestergaard, U.S. Pat. No. 3,989,672 describes an interfacial polycondensation polycarbonate process which cited both the Fry et al. and Moyer et al. patents as prior art. Vestergaard stated that molecular weight and the polydispersivity index were beneficially controlled by maintaining a reaction environment pH range of 8.0 to 10.2 during the polycondensation process.
Unexpectedly, the interfacial polycondensation process of this invention provides novel aromatic polycarbonates having a M.sub.w range of about 25,000-65,000 and a monocarbonate content of less than about 400 parts per million, subject to the proviso that the aromatic polycarbonates are prepared by an interfacial polycondensation polycarbonate process where the pH range is critically controlled and is initially and continuously throughout the polycondensation process maintained within the range of from at least 11 to about 13 prior to addition of any carbonyl halide, where the reaction environment is maintained at a temperature range of from 15.degree. C. to 40.degree. C., where the carbonyl halide is introduced at an average rate of about 0.03 to 0.3 moles/minute of carbonyl halide per mole of aromatic dihydroxy compound, and where a chain-stopper is present in amounts of 0.02 to 0.05 moles per mole of aromatic dihydroxy compound.
The process of this invention is unobvious since the process is generally carried out at phosgenation rates which are 3 to 300 times more rapid than those described in the Moyer, Jr. et al., Fry et al. or Vestergaard and is not limited to the use of any particular chain stopper or catalyst combination.